Field of the Invention
The present invention relates to fans and particularly high efficiency ceiling fans driven by a transverse flux motor.
Background
Fans are used in a wide variety of applications and most often are configured to move air in an effort to cool a room or object. Ceiling fans have become common place in homes and buildings and many of them run for long periods of time or continuously. Ceiling fans are driven by electric motors that are not very energy efficient, especially at the relatively low rotational speeds and comprise a large amount of metal. In addition, high volume low speed (HVLS) fans have become more widely used to cool large spaces, such as poultry farms, industrial areas including manufacturing areas, warehouses, and the like. These fans are typically configured to run at lower speeds than conventional home ceiling fans. Electric motors used to drive the HVLS fans have lower efficiency at low speeds and therefore are often times running well below their peak efficiency speeds.
Fans are also used to cool a wide variety of objects such as data centers and electronic components, such as microprocessors, for example. Many fans used to cool these objects generate a considerable amount of heat, thereby contributing to the heat that needs to be dissipated in these rather confined spaces.
The U.S. Department of Energy (DOE) will be placing electrical energy consumption regulations on ceiling fans, pursuant to the Energy Policy and Conservation Act (EPCA). Many of the current technologies used in ceiling fans will most likely not meet these standards and new, more efficient drive motors are needed. As described starting on page 53 of RIN: 1904-AC87, Energy Conversion Standard Rulemaking Framework Document for Ceiling Fans and Ceiling Fan Light Kits, published on Mar. 8, 2013 by the U.S. Department of Energy, the Office of Energy Efficiency and Renewable Energy Building Technologies Program:                The most common ceiling fan motor is a single-phase induction motor (permanent-split capacitor type) with an external rotor. The efficiency of such motors can be improved by increasing the size of (or the quality of steel used in) the stator and rotor stack, improving the lamination design, increasing the cross section of copper wiring, or operating the fan at reduced speed through capacitor speed control.        Most induction motors are mounted to the fan blades directly. This configuration is known as direct-drive and means that the fan and motor rotate at the same speed. In principle, ceiling fans could attach the fan blades to the motor via a geared mechanism that allows the fan blades to rotate at a different speed than the motor (a technology used in many industrial fans). This would enable higher motor speeds for a given fan RPM, which could increase overall efficiency.        The most efficient ceiling fans on the market have brushless direct current (BLDC) motors. BLDC motors are permanent magnet synchronous alternating current (AC) motors driven by a converter plus inverter combination control system. In this configuration, the motor displays characteristics of direct current motors; thus, they are called brushless direct current motors. Because there is no electrical current flowing in the rotor of a BLDC motor, there are no rotor energy losses, thereby resulting in greater efficiency. While a typical ceiling fan has an efficiency of about 40 Liters per second per Watt (L/s*W), (86 CFM/W), fans that have a BLDC motor are capable of efficiency ratings of more than 142 L/s*W, (300 CFM/W). These fans tend to be higher-end products, and the increase in efficiency is likely attributable not only to the motor type but also to other design features (e.g., the blade shape and number of blades). Another advantage of these motors is that they tend to be smaller and make less noise than those found in traditional ceiling fan motors. One disadvantage of BLDC motors is that the lifetime of the motor may be less than the lifetime of an induction motor due to the electronic controls required to run the BLDC motor.        
Motors are typically designed for high efficiency, high power density, and low cost. Brushless DC motors require complicated windings that require special equipment and add additional manufacturing costs. Most brushless DC motors have relatively few poles, such as four to eight. The complicated winding required limits the number of poles that can practically be designed into a brushless DC motor. While some motors are generally complicated in their assembly, so as to achieve higher performance characteristics, a design utilizing fewer components, or a well-engineered assembly, may provide a superior motor solution at a lower price point.
There exists a need for a fan that is highly efficient, efficient at low speeds, requires less material content, is lighter weight, generates less heat, can be easily manufactured in high volume and is affordable. The cost of most of the high volume fans currently being assembled today is in the material content. Electric motor production is highly automated and therefore labor and tooling are typically a low percentage of the overall cost of manufacturing. Reducing material content, such as the metal and magnets required will directly reduce the cost of the motor.